A point in the celestial sphere above the observer's head. Zenith

The celestial sphere is an imaginary spherical surface of arbitrary radius, in the center of which is the observer. Celestial bodies are projected on celestial sphere.

Due to the small size of the Earth, in comparison with the distances to the stars, observers located in different places on the earth's surface can be considered as being in the center of the celestial sphere. In fact, no material sphere surrounding the Earth exists in nature. Celestial bodies move in the boundless space of the world at various distances from the Earth. These distances are unimaginably great, our vision is not able to assess them, therefore, to a person, all celestial bodies appear to be equally distant.

During the year, the Sun describes a large circle against the background of the starry sky. The annual path of the Sun in the celestial sphere is called the ecliptic. Moving across ecliptic. The sun crosses the celestial equator twice at the equinoxes. This happens on March 21 and September 23.

The point of the celestial sphere, which remains motionless during the daily movement of the stars, is conventionally called the north celestial pole. The opposite point of the celestial sphere is called the south celestial pole. Residents of the northern hemisphere do not see it, because it is below the horizon. A plumb line passing through the observer crosses the sky overhead at the zenith and at the diametrically opposite point, called the nadir.

The axis of visible rotation of the celestial sphere, connecting both poles of the world and passing through the observer, is called the axis of the world. On the horizon below the north pole of the world lies north point, its diametrically opposite point - south point. East and West Points lie on the horizon line and are 90° apart from north and south points.

The plane passing through the center of the sphere perpendicular to the axis of the world forms plane of the celestial equator parallel to the plane of the earth's equator. The plane of the celestial meridian passes through the poles of the world, points of north and south, zenith and nadir.

Celestial coordinates

The coordinate system in which the reference is made from the plane of the equator is called equatorial. The angular distance of the star from the celestial equator is called , which varies from -90 ° to + 90 °. declination considered positive north of the equator and negative south. is measured by the angle between the planes of great circles, one of which passes through the poles of the world and the given luminary, the second through the poles of the world and the vernal equinox point lying on the equator.

Horizontal coordinates

Angular distance is the distance between objects in the sky, measured by the angle that is formed by the rays going to the object from the point of observation. The angular distance of the star from the horizon is called the height of the star above the horizon. The position of the sun relative to the sides of the horizon is called the azimuth. The countdown is from the south clockwise. Azimuth and the height of the star above the horizon is measured with a theodolite. In angular units, not only the distances between celestial objects are expressed, but also the sizes of the objects themselves. The angular distance of the celestial pole from the horizon is equal to the geographic latitude of the area.

The height of the luminaries at the climax

The phenomena of the passage of luminaries through the celestial meridian are called climaxes. The lower climax is the passage of the luminaries through the northern half of the celestial meridian. The phenomenon of the passage of the luminary of the southern half of the celestial meridian is called the upper climax. The moment of the upper culmination of the center of the Sun is called true noon, and the moment of the lower climax is called true midnight. The time interval between climaxes - half a day.

For non-setting luminaries, both climaxes are visible above the horizon, for ascending and setting lower climax occurs below the horizon, below the north point. Every star culminates in a given area is always at the same height above the horizon, because its angular distance from the celestial pole and from the celestial equator does not change. The sun and moon change height
which they culminate.

Origin

Word zenith came from an inaccurate reading of the Arabic expression سمت الرأس ( samt ar-ra's), meaning "direction to the head" or "way overhead". In the Middle Ages, during the 14th century, this word came to Europe through Latin and possibly through Old Spanish. It was shortened to samt("direction") - samt and with spelling errors transformed into senite - senit. Through the Old French and Middle English word senite finally turned into a modern word in the 17th century zenith .

Relevance and use

The concept of "zenith" is used in the following scientific contexts:

It serves as a direction for measuring zenith angle, which is the angular distance between the direction to the object of interest to us (for example, to a star) and the local zenith relative to the point for which the zenith is determined.
It defines one of the axes of the horizontal coordinate system in astronomy.

Thus, it is connected with the concepts of the elements of the celestial sphere - a plumb line and a circle of the height of the luminary.

Strictly speaking, the zenith is only approximately associated with the local plane of the meridian, since the latter is defined in terms of the rotational characteristics of the celestial body, and not in terms of its gravitational field. They coincide only for an ideal symmetric body of revolution. For the Earth, the axis of rotation does not have a fixed position (for example, due to constant movements of ocean water and other water resources), and the local vertical direction, determined through the gravity field, itself changes direction in time (for example, due to lunar and solar tides and ebbs).

Sometimes the term zenith refers to the highest point reached by a celestial body (Sun, Moon, etc.) in the process of its apparent orbital movement relative to a given observation point. However, the Great Astronomical Dictionary gives the following definition of zenith:

A point on the celestial sphere directly above the observer's head. The astronomical zenith is formally defined as the intersection of a plumb line with the celestial sphere. Geocentric zenith - the intersection with the celestial sphere of a line running from the center of the Earth through the position of the observer. The geodesic zenith is on a line normal to the geodesic ellipsoid or spheroid at the observer's position.

Thus, in relation to, for example, the Sun, the zenith can only be reached at low latitudes.

A point in the sky lying upward, in the direction of a plumb line, at every place on the earth's surface. In astronomy, in addition to this geographical Z., there is also a geocentric ... Encyclopedic Dictionary of Brockhaus and Efron

zenith - Zenith, pl. no, m. [from Arabic. samt - direction; arose by mistakenly reading the letter "m" for "ni"]. 1. The highest point of the celestial sphere, located above the head of the observer (astro). The sun is at its zenith. 2. trans. The highest degree of something. Large dictionary of foreign words

zenith - zenith, -a Orthographic dictionary. One N or two?

zenith - ZENIT a, m. zenith, German. Zenith<, лат. zenith. 1. астр., геогр. Солнце прямо в верху нашего зенита или главной точки стоит. Алярд 132. Зениф и надир, называются полы горизонтовы, и отстоят от горизонта в равном разстоянии. Кн. навиг. 2 7. | В сравн. Dictionary of Russian Gallicisms

zenith - Borrowed from French, where zenith is a paraphrase of the Arabic word semt, "road". See anti-aircraft gun. Etymological Dictionary of Krylov

zenith - noun, number of synonyms: 13 apogee 13 crown 19 top 34 peak 213 highest step 8 highest point 9 team 163 climax 12 society 61 limit 39 peak 10 degree 32 point 100 Dictionary of synonyms of the Russian language

zenith - Zenith /. Morphemic spelling dictionary

zenith - zenith I m. The highest imaginary point of the celestial sphere, located above the observer's head and opposite to the nadir (in astronomy). II m. The highest degree, the highest limit, the top of something. Explanatory Dictionary of Efremova

zenith - ZENIT m. Greek. a mental point in the sky, vertically above an earthly object or point; parietal point, tarsal. The continuation of this plumb line will pass through the center of the earth and mark the nadir on the opposite side of the imaginary firmament. Zenith, pertaining to the zenith. Dahl's Explanatory Dictionary

zenith - see >> apogee, highest Abramov's synonym dictionary

zenith - -a, m. 1. aster. The highest point of the celestial sphere above the observer's head. The sun is at its zenith. □ A gently sloping month is almost at its zenith, and from end to end over the native steppe a shimmering scattering of spring-like small stars. Sholokhov, Light and darkness. 2. trans. Small Academic Dictionary

zenith - A point on the celestial sphere directly above the observer's head. The astronomical zenith is formally defined as the intersection of a plumb line with the celestial sphere. Big astronomical dictionary

zenith - ZENITH, a, m. 1. In astronomy: a point on the celestial sphere, located vertically above the observer's head. 2. trans. The highest degree, the pinnacle of something. (high). At the zenith of glory. | adj. anti-aircraft, oh, oh (to 1 value). Explanatory dictionary of Ozhegov

Zenith - I Zenith (French zénith, from Arabic zemt, literally - path, direction) point of the celestial sphere (See Celestial Sphere), located above the observer's head; in the sky, the celestial sphere is crossed by a line directed vertically upwards from the place of observation. Great Soviet Encyclopedia

All heavenly bodies are at unusually large and very different distances from us. But to us they seem to be equally remote and as if located on a certain sphere. When solving practical problems in aviation astronomy, it is important to know not the distance to the luminaries, but their position on the celestial sphere at the time of observation.

The celestial sphere is an imaginary sphere of infinitely large radius, the center of which is the observer. When considering the celestial sphere, its center is combined with the eye of the observer. The dimensions of the Earth are neglected, so the center of the celestial sphere is often combined with the center of the Earth as well. The luminaries are applied to the sphere in such a position in which they are visible in the sky at some point in time from a given point of the observer's location.

The celestial sphere has a number of characteristic points, lines and circles. On fig. 1.1, a circle of arbitrary radius depicts a celestial sphere, in the center of which, indicated by the point O, the observer is located. Consider the main elements of the celestial sphere.

The vertical of the observer is a straight line passing through the center of the celestial sphere and coinciding with the direction of the plumb line at the point of the observer. Zenith Z - the point of intersection of the observer's vertical with the celestial sphere, located above the observer's head. Nadir Z" - the point of intersection of the observer's vertical with the celestial sphere, opposite to the zenith.

The true horizon N E SW W is a large circle on the celestial sphere, the plane of which is perpendicular to the vertical of the observer. The true horizon divides the celestial sphere into two parts: the above-horizon hemisphere, in which the zenith is located, and the sub-horizon hemisphere, in which the nadir is located.

The axis of the world PP" is a straight line around which the visible daily rotation of the celestial sphere takes place.

Rice. 1.1. Basic points, lines and circles on the celestial sphere

The axis of the world is parallel to the axis of rotation of the Earth, and for an observer located at one of the poles of the Earth, it coincides with the axis of rotation of the Earth. The apparent daily rotation of the celestial sphere is a reflection of the actual daily rotation of the Earth around its axis.

The poles of the world are the points of intersection of the axis of the world with the celestial sphere. The celestial pole, located in the constellation Ursa Minor, is called the North celestial pole R, and the opposite pole is called the South R.

The celestial equator is a large circle on the celestial sphere, the plane of which is perpendicular to the axis of the world. The plane of the celestial equator divides the celestial sphere into the northern hemisphere, in which the North Pole of the World is located, and the southern hemisphere, in which the South Pole of the World is located.

The celestial meridian, or the meridian of the observer, is a large circle on the celestial sphere, passing through the poles of the world, zenith and nadir. It coincides with the plane of the earth's meridian of the observer and divides the celestial sphere into the eastern and western hemispheres.

The north and south points are the intersection points of the celestial meridian with the true horizon. The point closest to the North Pole of the world is called the north point of the true horizon C, and the point closest to the South Pole of the world is called the south point Yu. The points of east and west are the points of intersection of the celestial equator with the true horizon.

Midday line - a straight line in the plane of the true horizon, connecting the points of north and south. This line is called noon because at noon, local true solar time, the shadow from the vertical pole coincides with this line, that is, with the true meridian of this point.

The southern and northern points of the celestial equator are the points of intersection of the celestial meridian with the celestial equator. The point closest to the southern point of the horizon is called the south point of the celestial equator, and the point closest to the northern point of the horizon is called the north point

The vertical of the luminary, or the circle of height, is a large circle on the celestial sphere, passing through the zenith, nadir and luminary. The first vertical is the vertical passing through the points of east and west.

The circle of declination, or the hourly circle of the luminary, PMP is a large circle on the celestial sphere, passing through the poles of the myoa and the luminary.

The daily parallel of the luminary is a small circle on the celestial sphere, drawn through the luminary parallel to the plane of the celestial equator. The visible daily movement of the luminaries occurs along the daily parallels.

Almukantarat of the luminary AMAG - a small circle on the celestial sphere, drawn through the luminary parallel to the plane of the true horizon.

The considered elements of the celestial sphere are widely used in aviation astronomy.